The present invention relates generally to a radially expandable endoluminal covered stent assembly and a method and apparatus for making the same. More particularly, the present invention relates to a longitudinally and radially expanded polytetrafluoroethylene (ePTFE) tubular graft which is circumferentially engaged about at least one balloon expandable endoluminal stent and retained on the stent by a radial recoil force exerted by the ePTFE tubular graft against the stent.
The covered stent may comprise one or more stents circumferentially retained within a single graft. For example, according to a first preferred embodiment of the invention, a covered stent is made using a single pressure expandable stent circumferentially and longitudinally covered with a single ePTFE tubular graft. In accordance with a second preferred embodiment, the covered stent comprises a pair of balloon expandable stents positioned at opposing ends of a single ePTFE tubular graft with each stent being circumferentially and longitudinally covered by the ePTFE graft, with an intermediate region of the ePTFE tubular graft being unsupported. According to a third preferred embodiment of the invention, a longitudinally articulating covered stent is made by co-axially aligning a plurality of discrete stents in a longitudinally extending array, such that the plurality of stents are in end-to-end relationship with one another, and the entire longitudinal array of stents is circumferentially and longitudinally covered with an ePTFE tubular ePTFE graft.
The present invention is further directed to a method for making the stent-graft assembly and for mounting the stent-graft onto a delivery catheter. In accordance with the method of the present invention, the stent-graft is assembled using a dilation mandrel and a stent mandrel. The inventive method includes the steps of mounting the stent onto the stent mandrel, joining the stent mandrel with the dilation mandrel, positioning the graft onto the dilation mandrel and radially expanding the graft on the dilation mandrel to an inner diameter which is greater than the outer diameter of the stent, passing the radially expanded graft over the stent, trimming excess graft material from the proximal and distal ends of the stent, decoupling the mandrel from the stent mandrel, and removing the covered stent from the stent mandrel. In accordance with the method of mounting the covered stent onto a delivery catheter, the method further includes the steps of disengaging a proximal section of the stent mandrel, engaging a delivery catheter with the stent mandrel such that a balloon section of the delivery catheter is proximate with the covered stent-graft, concentrically positioning the covered stent-graft over the balloon section of the delivery catheter and disengaging the delivery catheter from the stent mandrel.
Radially pressure expandable and self expanding endoluminal stents, such as those disclosed by Palmaz in U.S. Pat. Nos. 4,733,665, 4,739,762 and 5,102,417, Gianturco in U.S. Pat. Nos. 4,580,568 and 4,907,336, Kreamer in U.S. Pat. No. 4,740,207, Wlktor in U.S. Pat. Nos. 4,886,062 and 4,969,458, Pinchuck in U.S. Pat. No. 5,163,958 and Schatz in U.S. Pat. No. 5,195,984 have been clinically investigated over the past several years in an attempt to overcome the limitations of percutaneous transluminal coronary angioplasty (PTCA), particularly restenosis due to fibrocellular intimal proliferation subsequent to PTCA. More recently, investigations have focused on balloon-expandable stents to anchor intraluminal grafts. "Transfemoral Intraluminal Graft Implantation for Abdominal Aortic Aneurysms", Ann. Vasc. Surg. 1991, 5: 491-499; "Transluminal Placement of a Prosthetic Graft-Stent Device for Treatment of Subclavian Artery Aneurysm", J. Vasc. Surg., December 1993, 18:1056-1059; and "Percutaneous Femoropopliteal graft Placement", Radiology, June 1993, 187:643-648.
Several supported grafts are known in the art. For example, Kubo, et al., U.S. Pat. No. 5,236,447, disclose an artificial tubular organ supported by a supporting frame made of a plastic material, which may be PTFE, and a medical prosthetic material disposed on at least one surface of the supporting frame wherein the prosthetic material is preferably comprised of absorbable and non-absorbable macromolecular yarns which may include PTFE. The medical prosthetic material is joined to the supporting frame by sutures. The sutures attaching the prosthetic material to the supporting frame limit movement of the fabric on the frame. The Kubo, et al. assembly is not radially expandable and is therefore incapable of use in endoluminal applications which require radial expandability.
The Rhodes, U.S. Pat. No. 5,122,154 discloses an endovascular bypass graft comprising a sleeve having a plurality of expandable, ring-like stent members are equidistantly spaced along the longitudinal length and positioned on either the outer or inner surface of the sleeve. The sleeve is formed from a highly flexible material, such as expanded PTFE, and has a series of longitudinally extending pleats. Each stent member is connected to one or more of the longitudinally extending pleats in the sleeve and permit unfolding of the sleeve during radial expansion of the ring-like stent members.
Lee, U.S. Pat. No. 5,123,917, describes a radially expandable supported graft having multiple graft layers. The supported graft includes a flexible cylindrical inner tube having an outer periphery, a plurality of separate scaffold rings mounted on the outer periphery along the longitudinal extent of the inner tube, and a flexible cylindrical outer tube concentrically enclosing the inner tube and scaffold members. The scaffold members are spaced to allow for flexibility of the inner and outer tubes along their longitudinal axis.
Another endovascular graft for repairing aneurysms is described in U.S. Pat. No. 5,211,658 issued to Clouse. The Clouse patent discloses a percutaneously deliverable structural frame and an independently, percutaneously deliverable radially expandable tubular member subsequently placed concentrically within the structural frame. The structural frame preferably comprises a plurality of meshed strands joined to axially spaced end rings wherein both the meshed strands and rings are comprised of a shape memory metal. The tubular member, a thin walled flexible membrane, preferably includes a means for expanding and holding the tubular member against the structural frame. This means may take the form of an outwardly expansible spring coil disposed within the interior of the tubular member.
Kreamer, U.S. Pat. No. 5,078,726, discloses a stent-graft assembly having stents placed inside either one or more ends of a graft. The stents are formed from a rectangular semi-rigid material rolled into an open ended cylinder so that an inside longitudinal edge overlaps an outside longitudinal edge of the material. The stents further comprise a retaining means which acts to restrain the inner longitudinal edge of the graft in the graft's expanded state. In use, the synthetic graft is endoluminally positioned to exclude a weakened section of the vasculature. A stent in its relaxed diameter state is positioned inside the end of a graft and expanded to its enlarged, larger diameter state. The radially expansive force of the stent impinges upon the graft and the inner wall of the blood vessel to prevent displacement of the stent and graft after radial expansion.
Although a number of radially expandable stent-graft delivery systems are particularly suitable for endoluminal delivery and placement are generally known in the art, none of the foregoing radially expandable stent-graft assemblies offers a configuration which inhibits axial displacement of the graft relative to the stent prior to and during endoluminal delivery and radial expansion without the use of adhesives or sutures. Further, none of the previously known stent-graft devices reduces the profile of the stent graft combination thereby enabling the reduced French size of the introducer balloon catheter.
Accordingly, there is a need for a stent-graft assembly which permits use of a reduced size introduction catheter to facilitate easy and safe deployment of the stent-graft assembly within various sizes of blood vessels and at various sites within the blood vessels. There is also a need for a stent-graft assembly which comprises a graft which is retained upon a substantially non-radially expanded stent by inherent radial recoil forces exerted by the graft against the stent during delivery and radial expansion of the stent-graft assembly.